Angioscopic evaluation after venous stents

Lower extremity woven and nonwoven venous stent morphology and luminal changes

OBJECTIVE

Venous stents are a common treatment modality for obstructive venous disease. Venous stents differentiate themselves by either a woven or braided structure, open or closed cell arrangement or based on material composition (elgiloy vs nitinol). Changes in the morphology of venous stents over time may contribute to restenosis or thrombosis. Woven elgiloy stents are prone to proximal and distal edge deformation compared with dedicated venous stents, which offer increased radial force at stent edges. The objective of this study is to describe luminal morphological changes among various venous stents and between woven to nonwoven venous stent configuration, over time.

METHODS

A retrospective review at a single institution between January 2014 and June 2021 identified patients treated with venous stents. Patients with iliac and/or femoral venous stents with intraoperative intravascular ultrasound and a postoperative computed tomography scan were included in the study. Cross-sectional diameters measurements were taken at proximal, middle, and distal portions of each stent from intravascular ultrasound examination at the time of initial stenting and compared with the cross-sectional diameter measurements taken from computed tomography imaging at follow-up. A paired t test was used to compare the luminal change with a D'Agostino-Pearson test used for normality.

RESULTS

Fifty-four stents distributed among 38 patients were identified. The mean time to follow-up was 17.5 months. Stents were placed in the common iliac vein (n = 37, 68.5%), external iliac vein (n = 14, 25.9%), and common femoral vein (n = 3, 5.6%). Implanted stents included the Boston Scientific Wallstent (n = 23, 42.6%), Bard Venovo (n = 3, 5.6%), Boston Scientific Vici (n = 23, 42.6%), and Medtronic Abre (n = 5, 9.3%). The mean luminal loss was measured at 2.12 mm proximally (95% confidence interval [CI], 1.64-2.60; P<.001), 1.29 mm at the mid-stent (95% CI, 0.83-1.74, P<.001), and 1.56 mm distally (95% CI, 0.99-2.12; P<.001). There was no significant difference in luminal changes between woven and nonwoven stents at proximal (P = .374), middle (P = .179), and distal (P = .609) stent measurements.

CONCLUSIONS

This study reports morphological changes within venous stents and between woven and nonwoven venous stents. Our findings demonstrate that the edge-stent luminal decrease traditionally attributed to woven configurations also occurs with the newer nonwoven stents. Additional factors such as anatomical location, pelvic curvature, and other external forces may be accountable for this change rather than geometrical configuration of the stent.

The impact of stent protrusion into the inferior vena cava or jailing of the contralateral iliac vein on the incidence of contralateral deep vein thrombosis following venous stenting

OBJECTIVE

Iliac vein stenting is the standard of care for patients with pelvic venous disorders secondary to symptomatic iliac vein outflow obstruction. Venous stents are often extended proximally into the inferior vena cava (IVC) which may result in partial or complete coverage of the contralateral iliac vein. The purpose of this investigation is to determine if extension of iliac vein stents into the IVC results in increased risk of contralateral deep venous thrombosis (DVT).

METHODS

We retrospectively reviewed prospectively collected data from 409 patients who underwent iliac vein stenting at the Center for Vascular Medicine (CVM) from 2019 to 2020. Stent type, covered territories, initial and follow-up consults, ultrasound and operative reports were reviewed to assess for incidence of post-implantation DVT. Patients were stratified into three groups: Iliac vein stents which protruded into the IVC, stents that completely covered the orifice of the contralateral iliac vein and those with no stent protrusion into the IVC.

RESULTS

Out of 409 patients, the average age was 53.96 ± 13.40 years with 94 males and 315 females. All stents placed were Venovo stents and all iliac vein lesions were non-thrombotic stenoses. The average follow-up period was 14.35 ± 10.09 months. The most common territories stented were the IVC-LCIV-LEIV (n = , 74%) and the IVC-RCIV-REIV (n = , 26%). Stent protrusion and distance into the IVC in millimeters (mm) was the following: Partial protrusion (n = 314, 77%, 27.6 ± 19.1), jailing of the contralateral iliac vein (n = 78, 19%, 45.9 ± 18.6), no protrusion (n = 16, 4%). The overall DVT rate post-implantation was 0.49% (n = 2). No DVTs ipsilateral to the index stent were identified and both DVTs were contralateral DVTs. A hypercoaguable disorder was reported in 6 patients (1.5%). There were no significant differences in prevalence of contralateral DVT between the three groups. (p = .35).

CONCLUSION

The rate of contralateral DVTs post iliac vein stenting with Nitonol based stents is extremely low. Partial or complete coverage of the contralateral iliac vein via stenting does not result in an increased incidence of contralateral DVT in the short-term. Longer follow up is needed to determine if contralateral DVTs occur after long-term implantation.

Histological Features of In-Stent Restenosis after Iliac Vein Thrombus Removal and Stent Placement in a Goat Model

PURPOSE

To establish an animal model for in-stent restenosis (ISR) after postthrombotic iliac vein stent placement and characterize histopathological changes in tissue within the stented vein.

MATERIALS AND METHODS

Iliac vein thrombosis was induced using balloon occlusion and thrombin injection in 8 male Boer goats. Mechanical thrombectomy and iliac vein stent placement were performed 3 days after thrombosis induction. Restenosis was evaluated by venography and optical coherence tomography (OCT) at 1 and 8 weeks after stent placement, and stent specimens were taken for pathological examination after the animals were euthanized.

RESULTS

Thrombosis induction was successful in all 8 goats, with >80% iliac vein occlusion. After thrombus removal, OCT revealed considerable venous intimal thickening and a small number of mural thrombi. Neointimal hyperplasia with thrombus formation was observed in all goats 1 week after stent implantation; the degree of ISR was 15%-33%. At 8 weeks, the degree of ISR was 21%-32% in 3 goats, and stent occlusion was observed in 1 goat. At 1 week, the neointima predominantly consisted of fresh thrombi. At 8 weeks, proliferplastic fibrotic tissue and smooth muscle cells (SMCs) were predominant, and the stent surfaces were endothelialized in 2 of 3 goats and partially endothelialized in 1 goat.

CONCLUSIONS

In the goat model, postthrombotic neointimal hyperplasia in the venous stent may result from time-dependent thrombus formation and organization, accompanied by migration and proliferation of SMCs, causing ISR. These results provide a basis to further explore the mechanism of venous ISR and promote the development of venous stents that reduce neointimal hyperplasia.